Insights into the mechanism of hydrogen peroxide activation with biochar produced from anaerobically digested residues at different pyrolysis temperatures for the degradation of BTEXS

Abstract

The disposal of large amounts of biogas residue from anaerobically digested waste is a burden on environment protection. Porous biochars (BCs) were synthesized from biogas residue at three pyrolysis temperatures (300 °C, 550 °C, and 800 °C) and used to catalyze H₂O₂ for the degradation of benzene, toluene, ethylbenzene, xylene isomers (ortho, para, and meta), and styrene (BTEXS) to develop a new use for biogas residues. The prepared BCs were characterized through scanning electron microscopy, Brunauer-Emmett-Teller method, Fourier transform infrared spectrometry, and X-ray photoelectron spectroscopy. Results showed that BC800/H₂O₂ had the highest BTEXS degradation performance over 6 h. The degradation kinetic data were most consistent with the pseudo-second-order model. The different catalytic effect of the three BCs pyrolyzed at different temperatures were attributed to the dominant active sites (C-O/C-OH/C=C/C=O groups, pyridinic N, and graphitic N) that induced the production of reactive oxygen species (ROS). ROS-quenching experiments indicated that the degradation of BTEXS by BC300/H₂O₂, BC550/H₂O₂, and BC800/H₂O₂ involved ∙OH, ∙O₂^-, and ¹O₂. ∙OH was the dominant ROS in BC300/H₂O₂ and BC550/H₂O₂, and ¹O₂ was the dominant ROS in BC800/H₂O₂. Our findings provided new insight into the different catalytic mechanisms for BC production at different pyrolysis temperatures and demonstrated that a porous BC catalyst with high utilization value could be prepared from biogas residue and could hold considerable potential for application in BTEXS treatment in the future.

Keywords: BTEXS; Biochar; Biogas residue; Pyrolysis temperature; Reactive oxygen species; Surface feature.